Rigid polyurethane foam has been prepared by the reaction of a polyfunctional isocyanate with a polyol such as a polyester polyol, polyether polyol or the like using a foaming agent in the presence of an amine catalyst, metal catalyst or the like. Useful rigid foams typically have good adiabatic and lightweight structural properties. Therefore, rigid foams can widely be used as heat insulating materials, building materials, structural materials and the like materials.
Previously, in case of the preparation of rigid polyurethane foam, there have been used as blowing agents chlorofluorocarbons such as CFC-11 or CFC-12 and water. Recently from the view point of environmental destruction, the use of chlorofluorocarbons have been restricted. It is desired that the blowing agents comprise water alone, or in case of a combination of chlorofluorocarbon and water, a large quantity of water and a minimum amount of chlorofluorocarbon.
However, when water alone or a large quantity of water is used as a blowing agent, water reacts predominantly with isocyanate to form highly crystalline urea bonding instead of the desired reaction of the isocyanate with a polyol. This results in the deterioration of, for example, dimensional stability, friability, adiabatic and adhesive properties. In order to overcome these problems processes using a polymer polyol prepared by the polymerization of an ethylenic unsaturated monomer in a polyol are disclosed in JP 90/281,021, JP 91/287,639 and JP 92/239,516; but the prevention of the deterioration of physical properties has not been satisfactory.